I have a 1971 Rolex GMT, original owner. I am posting in this forum because my question pertains to watches in general. The watch was serviced in June of 2014 and has been running 1 to 2 seconds fast per day.
A few weeks ago it began to gain 4 to 5 seconds per day and has been consistent at that rate since. It has not been dropped or received any rough treatment, my wearing pattern has not changed nor does it show any signs of moisture in the case. I wear it at night and positional deviation does not seem to be a factor. I believe if magnetized it would show a much larger rate deviation.

My local guy who has maintained it since the 70's retired and I have not found anyone I would trust to open the case and investigate.

Any watch professionals on this forum have an opinion on what may have caused this change?